Dry-erase surface composition and method of applying

ABSTRACT

A dry erase writing surface is formed from a single component, 100% solids polyurethane, ambient cured, dry erase paint composition having at least ninety percent by weight low NCO isocyanate, a cure accelerating catalyst and a defoaming agent. The surface is ready for use in a day. The composition can additionally contain a diluent, vegetable oil or mineral spirits. The coating has a VOC of between 0 and 49 g/l. The coating is initially applied to the surface of the substrate to form a film thickness of 1-3 mils. The whiteboard is characterized as when tested by erasure of the dry erase markers, the marks are virtually invisible after 2500 cycles. The composition can be packaged as a kit with applicators.

FIELD OF THE INVENTION

This invention generally relates to a dry erase writing surface. Moreparticularly, the invention relates to a single component, 100% solidspolyurethane, ambient cured, dry erase paint and a method for convertinga conventional wall or other surface to a surface having thecharacteristics of a manufactured dry erase surface.

BACKGROUND OF THE INVENTION

Dry erase surfaces have virtually replaced chalkboards as the preferredwriting surface for corporate use, training centers, schools, and a widerange of other end uses. Dry erase surfaces are most commonly providedin pre-manufactured board sizes. Conventional dry erase surfaces includeporcelain, ceramic, melamine, and polyvinyl chloride (PVC). Dry erasePVC based wall coverings can also be used to create a dry erase surface.Other known dry erase coatings are two-part epoxy coatings. For example,U.S. Pat. No. 6,265,074, issued to Shah, et al. discloses a dry erase,two part epoxy coating that is applied to a flexible substrate to whichan adhesive is applied. Similarly, U.S. Pat. No. 6,312,815 issued toMacris et al. and U.S. Pat. No. 4,716,056 issued to Fox et al. disclosetwo-part epoxy coatings that may be applied to treated and untreatedsurfaces. Two-part epoxy type coatings are impractical in the field,requiring highly skilled labor and specific equipment for mixing andapplication. Furthermore, once the two parts of the epoxy are mixed, theproduct has a very limited pot life measured in hours, not days orweeks. Other coatings “proposed” for dry erase applications specify theybe either in a water-based carrier or a solvent-based carrier.

Other methods of producing dry erase surfaces include fire-coatedglazes, such as that disclosed in U.S. Pat. No. 4,123,590 issued toHasegawa et al. As disclosed by U.S. Pat. No. 5,037,702, issued to Pittset al., other one part coatings in the art require specialized curingsuch as high temperatures, ultraviolet (UV), and/or electron beam (EB)curing lights in order to exhibit favorable dry erase characteristics.For example, U.S. Pat. No. 6,103,327 issued Bragole et al. discloses athermally cured paint. White is the predominate color being sold andutilized.

Pre-manufactured dry erase boards provide varying levels of performanceover their life, depending on the writing surface used. With the lessexpensive melamine boards, performance is compromised for a lower price.The primary limitation on all pre-manufactured dry erase boards is thata customer is limited to only the sizes offered. While a dry erasewallcovering can be installed to cover an entire wall surface, corner tocorner and floor to ceiling, a dry erase wallcovering requires anexpensive installation utilizing skilled labor. Failure of the dry erasesurface of the wallcovering will require removal of the dry erasewallcovering, wall preparation, and re-hanging new a dry erasewallcovering.

The inks of the typical, dry erase markers, such as Sanford Expo dryerase marker (Sanford Division of Newell Rubbermaid, Inc., 2707Butterfield Road, Oak Brook, Ill. 60523) will not penetrate a dry erasesurface, thereby erasing is accomplished with minimal effort. Thosestandard markers will not “ghost”, and cleaners, such as Sanford BlueExpo white board cleaner (containing 2-Butoxy Ethanol/Acetate, IsopropylAlcohol), may be used to maintain dry erase surfaces.

BRIEF SUMMARY OF THE INVENTION

The invention comprises a single component, 100% solids polyurethane,ambient cured, dry erase paint that may be applied to a surface byconventional painting techniques including brushing or rolling, toimpart or improve the dry erase characteristics of the surface. It isneither a solvent-based nor a water-based composition. The claim ofsolvent free is based on VOC's being below the limit of detectability ofEPAS method 24. The VOC is between 0 and 49. The dry erase paint of thepresent invention may be applied to many surfaces including gypsum wallboard, chalkboards, whiteboards, dry erase PVC wallcoverings and otherplastic surfaces, metal, medium density fiberboard (MDF), masonry,stone, and any number of other wall or display surfaces. If desired, adiluent can be employed with the polyurethane to achieve a desiredviscosity. The dry erase paint of the invention is typically dry totouch in around eight hours and the surface is usable within a day (24hours) depending on conditions. The open time of the dry erase paint ofthe invention is typical of latex paint, e.g. 4-5 hours. A singlecomponent coating for the purposes of the invention is one which isready to use without premixing in contrast to a two-component coatingmaterial where, owing to high reactivity of, binder component andcrosslinker components have to be kept in separate vessels. The twocomponents are not mixed until shortly before application, when theyreact generally without additional activation. A “solvent free one partcoating composition” of the invention is also intended to be water-freein the sense of not being a solvent-based or water based composition.

The paint of the present invention has inherent properties of hardness,moisture resistance, chemical resistance, and abrasion resistance whichtogether produce a superior dry erase surface. It cures, under ambientconditions, to a glossy hard shell finish that provides a durable dryerasable painted surface. The surface hardens as the formulation of thedry erase paint continues to cross link and harden, typically requiringa 24 hour minimum curing time before the surface can be used. This canvary since ambient conditions are employed. In contrast, most twocomponent systems, which require a separate catalyst, require seven daysbefore the surface is ready for marker use.

The dry erase paint of the present invention exhibits superior releaseproperties; meaning that a standard dry erase marker, such as theSanford Expo BOLD, LOW ODOR, or BULLET dry erases markers (SanfordDivision of Newell Rubbermaid, Inc., 2707 Butterfield Road, Oak Brook,Ill. 60523) will not penetrate the surface, thereby permitting erasureof the marks with minimal effort. When used with the formulation of thepaint of the present invention, those standard markers will not “ghost”,i.e. leave residual marks. The dry erase paint of the present inventionmay be used by any commercial painting contractor and particularly lendsitself to home and other do-it-yourself applications, who are unlikelyto invest in the costly equipment required for two-part epoxy finishesor prohibitively expensive curing systems required for other one partcompositions, such as UV and EB.

While white is typically the color of choice for dry erase displays, thedry erase paint composition of the present invention is available as aclear coating to be applied over any color substrate, or it is amenableto receiving tints and pigments so that the final dry erase surface mayhave an unlimited color selection suitable for the desired displayapplication. The coating can be transparent or tinted to an unlimitednumber of translucent or opaque colors if made with pigments or pigmentdispersions free of water and hydroxyl content. For example, a displayconveying warnings may be colored red and a display conveying safetyinformation may be colored green. In an educational or corporateenvironment, team or institutional colors may be popular choices.

The “white board” paint of the invention can, if desired, be packaged inkit form. The components of the kit can include written instructions,paint applicator, e.g. brush, roller, foam applicator, etc. The actualcomponents included in the kit are based on a desired application. Thekit can also be packaged to include material and material amounts whichare suitable for repair of a preexisting whiteboard. The amount of paintincluded in the container can be based on the surface to be treated.Since there is no premixing requirement like two-component systems (onesthat include a separate catalyst or agent), any unused paint can besaved for further use in the original container by resealing thecontainer.

As with any painting project, the surface being painted should be freeof dirt, oils, debris, and other contaminants. The area surrounding thesurface to be painted should be substantially free of residual dust,particulates, or other construction debris floating in the air becausethey may adhere to the paint and create unwanted particles that would bedetrimental to the suitability of the resultant dry erase writingsurface. A smooth surface is desired; any pretreatment, e.g. sanding,spackling, etc., should be attended to prior to application of thepaint.

To obtain the best results, a suitable primer coat should be applied tothe surface prior to applying the paint of the present invention. Intests, a coat of Zinser Prime Coat 2 acrylic latex primer was applied todrywall and permitted to dry for 24 hours before applying the paint ofthe present invention.

A moderate coat of the dry erase paint of the present invention may beapplied to the substrate by any conventional painting methods such asbrushing or rolling. But the best results were experienced by rollingusing a closed-cell melamine foam roller cover, supplied by Quali-TechMfg. Because the dry erase paint produces very minimal odor and has aVOC (volatile organic compounds), of between zero and 49 g/l, the dryerase paint can be applied in occupied spaces just like standard latexinterior paint, as long as the proper ventilation is present. A suitablysmooth dry erase surface may be obtained with a single coat of the dryerase paint applied with a high density foam roller, such as thoseprovided by Quali-Tech Mfg., which minimizes coating thickness andinsures surface smoothness. Ideally this application technique willachieve a desired coating thickness of between about 1-3 mils. If toolight a coat is applied the desired dry erase properties arecompromised. Whereas, application of too heavy a coat causes the curingtime to be extended and the coverage area for a given volume of paintreduced. Ideally a single coat is applied at the desired thickness.

After the dry erase paint has been applied to the substrate, theresulting dry erase writing surface should be allowed to dry for atleast 24 hours (1 day) before using. The drying times depend onconditions. It is possible to prepare a surface suitable for use in 24hours. The surface can be dry to the touch in just eight hours. Thedrying time period allows the necessary cross linking to take placeresulting in a high performing writable/erasable surface.

Unlike conventional dry erase boards and surfaces, should the paintedsurface contemplated by the present invention ever fail to perform dueto mistreatment or accidental damage, the surface can be readilyre-painted, bringing the surface back to its original level ofperformance. Indeed, the dry erase paint of the present invention may beused to repair or restore a conventional dry erase surface that had beendamaged or otherwise had its dry erase properties diminished throughexcessive, and in some instances routine use. This is a much moreeconomical repair than conventional methods, particularly with respectto PVC dry erase wallcoverings that typically require the completeremoval of the wall covering, repairing and prepping the wall surface toa level five finish, and re-hanging the PVC dry erase wallcovering.

The coating has additional uses, such as anti-graffiti coating, cleanroom coating, industrial wall, and educational wall and floor coatings.The treatable surfaces include properly prepared gypsum board, chalkboard, whiteboard, metal, glass, fiberboard, concrete, stone, wood andtile.

DETAILED DESCRIPTION OF THE INVENTION

Normally pure Isocyanate in a range above 90% of the total coatingformulation is not considered a viable coating option due to a varietyof factors. Isocyanate by itself will not dry or cure in a reasonabletime period when applied, so components such as driers and catalystsmust be added. However, adding a mineral spirit-like solvent or avegetable oil, e.g. sunflower oil, to Isocyanate as a diluent and flowand leveling agent addresses the drying and curing issues. This solutionwas not apparent in the prior art. The fact that an isocyanate has beenmodified with sunflower oil and then packaged without gelling,solidification or viscosity increase is an achievement. Normally, thehydroxyl content in the oil is naturally reactive with isocyanates, theresults of which create increased viscosity and solidification in thecan. Additionally, the coating formulation can be made without the useof a diluent, such as mineral spirits or vegetable oil. This simplermethod of making the dry erase coating is as effective as the coatingsmade with a diluent. The advantages of eliminating the diluent arethree-fold: The VOC drops to 5 g/l or less, the coating becomes a 100%solids formulation, and the coating contains none of the restrictedchemical components: acrolein, acrylonitrile, antimony, benzene, butylbenzyl phthalate, cadmium, di (2-ethylhexyl) phthalate, di-n-butylphthalate, di-n-octyl phthalate, 1,2-dichlorobenzene, diethyl phthalate,dimethyl phthalate, ethylbenzene, formaldehyde, hexavalent chromium,isophorone, lead, mercury, methyl ethyl ketone methyl isobutyl ketone,methylene, chloride, naphthalene, toluene (methylbenzene),1,1,1-trichloroethane and vinyl chloride.

Four factors contribute to the avoidance of gelling, solidification orviscosity increase: 1) A low hydroxyl content in the oil; 2) Thereaction of the remaining hydroxyl groups in the alkyd with the moisturescavenger before blending with the isocyanate; 3) The use of a lower NCOcontent isocyanate; and 4) a lower NCO content isocyanate which has alower degree of crosslinking and reactivity, therefore a reducedviscosity increase.

Isocyanate as the main coating component will generate carbon dioxideoff gassing, creating foaming in the finished coating. The foaming canbe read as bubbles, which not only create a visually poor surface, butthey compromise performance in that they leave open areas (pores) andcreate difficult to clean texture in the coating surface. Foamingassociated with this coating can be controlled in a variety of ways. Oneof the critical factors of foaming is the percent of the NCO content ofthe formulation. The Bayhydur 302, and other compatible ISO's, e.g. BASFHA 200, have an NCO content of 17% (17.3+/−0.5% per specification) orless. The desired isocyanates have a viscosity between 500 and 2500centipoise. Many isocyanates that might be candidates for our coatingcan have an NCO content in excess of 20%. In addition to incorporating alow NCO content isocyanate, a diluent, e.g. vegetable oil, can becombined with the Isocyanate. Of the vegetable oils, Sunflower oil ispreferred. Assuming the sunflower oil is 100% by weight solids, thediluted NCO content is 16.4% based on a weighed average of a blend of 95parts isocyanate and 5 parts oil. Foaming is proportional to NCO contentas one NCO moiety reacts with atmospheric water to produce one moleculeof carbon dioxide gas.

Sunflower oil is preferred because of its low yellowing tendency. Othersuitable vegetable oils include soybean oil, linseed oil, safflower oiland other drying oils. Near 100% solids alkyds might also be appropriateas a diluent.

Since bubbling relates, in part, to NCO concentration, it can becontrolled. With the proper ratio of Isocyanate, catalyst, and Byksiloxane, the coating can also be applied virtually bubble free.Further, the suggested diluent options, mentioned above, are effectivein altering the viscosity of the coating.

A second contributing factor to foaming is film thickness. Lowerviscosity and consistent application thickness reduce foaming. Theslight modification with sunflower oil and the siloxane additive helpproduce lower, more consistent film thickness and also helps with thedefoaming and carbon dioxide release properties of the coating.

By requiring the use of a high density, melamine foam roller cover forthe coating application, one is also able to control film thickness andthe ultimate surface smoothness. By maintaining a wet film thickness of1-3 mils (Calculated film thickness at 200 square feet per quart is 3mils) the foaming aspect of the isocyanate is kept in check.

The mixer used is a high-speed disperser with a toothed steel orstainless steel blade. The teeth are typically triangular orrectangular, perpendicular to the circumference of the blade, andalternate being turned up and down. Optimum blade tip speed is 4800 to5300 feet per minute. Optimum blade diameter is ⅓ of the batch tankdiameter with the blade immersed ½ the depth of the liquid. Optimumpower is about 1/10 HP per gallon. (These requirements can be modifiedor relaxed for the production of a clear, unpigmented coating.)

The examples which follow detail step by step preparation of a pigmentedpremix, which after standing overnight so that any moisture and hydroxylcontent is consumed, is added to the isocyanate. The final ingredient isline 18. In addition to the moisture scavenger, the process is conductedunder dry atmosphere, which may be used from the beginning. However,this is less critical. The dry erase surface is tested by erasure of thedry erase markers and the marks are virtually invisible after 2500cycles.

EXAMPLE 1

The one part coating where a vegetable oil is present as a diluent wasprepared as follows. The preferred amount is set forth in terms ofparts. Amounts within the range are expected to produce the desiredresults and purpose.

Ingr./Instr. Parts Range Description Purpose Combine the following, highspeed disperse for 10 minutes Sunflower oil 4.622 1.000- Sunflower oil.[Substitute: possible alternatives include Reactive diluent 40.000 oneor more of the following but are not limited to tall oil fatty acid, soybean oil, linseed oil, safflower oil, and other drying oils] Zirconiumcatalyst 0.023 .010- Zirconium carboxylate, solution of, 24% zirconiumPolymerization catalyst 1.000 content [Substitute: zirconium octoate ornaphthenate] Cobalt catalyst 0.023 .010- Cobalt carboxylate, solutionof, 12% metal content Autooxidation catalyst 1.000 [Substitute: cobaltoctoate or naphthenate] Then add and mix 20 minutes. Allow to standovernight. Dabco T12 0.051 0.000- Dibutyltin dilaurate [Substitute: Tinoctoate or bismuth Catalyst to accelerate 1.000 octoate] cure Incozol 20.046 0.000- 3-ethyl-2-methyl-2-(3-methylbutyl)-1, 3-oxazolidineDessicant 2.000 [Substitute: benzenesulfonyl isocyanate, 4-methyl-]Allow to stand 24 hours Add the above premix while mixing under dryatmosphere to: Bayhydur 302.1 83.304 30.000- Homopolymer ofhexamethylene diisocyanate Primary resin/polymer 100.000 Bayhydur 302.211.856 3.500- Polyisocyanate based on polyether modified 18.000hexamethylene diisocyanate Then add Byk 322 0.074 0.100- Aralkylmodified polymethylalkylsiloxane Surface tension reduction 2.000 anddefoaming additive Mix 10 minutes Cast three mil film; check forcraters, trash, film clarity, and color. Fill under dry atmosphere100.000

EXAMPLE 2

The one part coating where a vegetable oil is present as a diluent wasprepared as follows. The preferred amount is set forth in terms ofparts. Amounts within the range are expected to produce the desiredresults and purpose.

Ingr./Instr. Parts Range Description Purpose Combine the following, highspeed disperse or media mill to 7 Hegman fineness of grind Alkyd 0.5001.000- Alkyd being a condensation polymerization product of a Reactivediluent 40.000 fatty acid and a polyol. Acceptable fatty acids includeone or more of the following but are not limited to tall oil fatty acid,soy bean oil, linseed oil, or safflower oil. Polyols may include but arenot limited to glycerol, ethylene glycol, or pentaerythritol.Polyurethane alkyd 3.000 1.000- Aliphatic urethane modified alkyd beingan extension Reactive diluent 40.000 polymerization product of an alkydand an aliphatic isocyanate monomer such as hexamethylene diisocyanateor isophorone diisocyanate. Titanium dioxide 2.000 0.000- Titaniumdioxide pigment, micronized, paint grade, White pigment 25.000 suitablefor gloss paints and coatings. Aprotic solvent(s) 3.000 1.000- One ormore aprotic solvents selected from, but not Solvent 50.000 limited tomixed isomers of xylene (CAS #1330-20-7), aromatic naphtha (64742-95-6),light aliphatic solvent naphtha (64742-89-8), stoddard solvent(8052-41-3), tertiary butyl acetate (540-88-5), dimethyl carbonate(616-38-6) Organoclay 0.050 .100- Micronized pigment comprised oforganically treated Antisettling/antisag 5.000 hectorite clay[Substitute: amorphous fumed silica with additive surface area of200-380 m2/g] Driers 0.010 .010- One or more metallic driers selectedfrom but not Oxidative catalyst 1.000 limited to naphthenates oroctoates of cobalt or zirconium Fluoropolymer 0.080 0.00- Micronizedpolymer of tetrafluoroethylene, 5.000 perfluoroalkoxy, or fluorinatedethylene propylene. Then add and mix 20 minutes. Allow to standovernight. Dabco T12 0.050 0.000- Dibutyltin dilaurate [Substitute: Tinoctoate or bismuth Catalyst to accelerate 1.000 octoate] cure AdditiveTI 0.077 0.000- Benzenesulfonyl isocyanate, 4-methyl- [Substitute:Dessicant 2.000 oxazolidine] Allow to stand 24 hours Add the abovepremix while mixing under dry atmosphere to: Bayhydur 302.1 80.80030.000- Homopolymer of hexamethylene diisocyanate Primary resin/polymer100.000 Bayhydur 302.2 11.500 3.500- Polyisocyanate based on polyethermodified 18.000 hexamethylene diisocyanate Then add Diisocyanate Byk 3200.135 0.100- Polyether modified polymethylalkylsiloxane, solution Flow,leveling, and 2.000 defoaming additive Mix 20 minutes Cast three milfilm; check for craters, trash, film clarity, and color. Fill under dryatmosphere 101.20 2

EXAMPLE 3

Combine the following using a high speed mixer for 10 minutes todisperse the ingredients under a dry atmosphere:

99.85% Isocyanate (Bayhydur 302)  .096% Catalyst (Dabco T-12)  .059%Silicone (Byk 320)

Fill the remainder into a container under dry atmosphere.

While the amounts are set forth as specified percentages, the amountsshould be considered as approximately (about) the specified value.

If diluent is desired, odorless mineral spirits or equivalent can bepresent in an amount around 4%.

Although the invention has been described and illustrated in detail, itshould be recognized changes which depart from the specifics of theexamples and other taught embodiments are possible without departingfrom the spirit of the invention as described above. The spirit andscope of the present invention are to be limited only by the terms ofthe claims which follow.

The invention claimed is:
 1. A kit for preparing a surface which has dryerase properties comprising a container including therein a solvent freedry erase paint composition, characterized as a one component coating,consisting essentially of between 98-99.85% by weight of an isocyanate,a cure accelerating catalyst and a defoaming agent, wherein theisocyanate has a NCO content of about 17% or less, the cure acceleratingcatalyst and defoaming agent are present in amounts which produce a filmthickness on a substrate, when still wet, of 1-3 mils, which upon dryingfor at least 24 hours at an ambient temperature forms a dry erase bubblefree surface that is ready for use and where marks formed on the surfaceby dry erase markers are virtually invisible after 2500 cycles.
 2. Thekit according to claim 1 further comprising a roller and/or brush. 3.The kit according to claim 1 further comprising materials and writteninstructions for affecting repairs and/or surface treatment.
 4. The kitaccording to claim 1, wherein the container includes an inert gas withthe composition.
 5. A kit for preparing a surface which has dry eraseproperties comprising a container including a solvent free dry erasepaint composition comprising between 98-99.85% by weight of anisocyanate, a cure accelerating catalyst, a defoaming agent and adiluent, wherein the isocyanate has a NCO content of about 17% or less,the cure accelerating catalyst and defoaming agent are present inamounts, which produce a film thickness, when still wet, of 1-3 mils,which upon drying at an ambient temperature for at least 24 hours formsa dry erase bubble free surface that is ready for use and where marksformed by dry erase markers are virtually invisible after 2500 cyclesand wherein the paint composition is a one component coating.
 6. The kitaccording to claim 5 wherein the diluent is odorless mineral spirits orvegetable oil.
 7. The kit according to claim 1, Wherein the cureaccelerating catalyst is selected from dibutylin dilaurate, tin octoateor bismuth octoate and the defoaming agent is siloxane.
 8. The kitaccording to claim 1, wherein the composition has a VOC of less than 5g/l.